Mirror grinding method and glass lens

ABSTRACT

A mirror surface grinding method processes an optical glass material into a lens shape using a cup-shaped grinding stone. The grinding stone is pupplied with a polishing solution which contains charged fine particles, thereby electrically attaching the charged fine particles to the grinding stone. The grinding stone is rotated and moved relative to the optical glass material along a final shape to be generated from the optical glass material, thereby grinding an unnecessary portion of the optical glass material to remove it, using a peripheral face portion of the grinding stone, and at the same time polishing the final shape surface of the optical glass material using charged fine particles attached to an annular face portion of the rotating and moving grinding stone.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a grinding method using thefine-particle electrophoresis phenomenon, and to a glass lens worked bythe grinding method.

[0002] A grinding method using the electrophoresis phenomenon is knownfrom, for example, documents “Research Concerning Grinding Method UsingElectrophoresis Phenomenon of Ultra-fine Particles” published in a 1996spring convention of The Japan Society for Precision Engineering.

[0003] The documents describe a grinding device for grinding an objector workpiece 25 so that its surface becomes flat, which comprises, as isshown in FIG. 17, a cup-shaped grinding stone 20 rotatable about itsaxis of rotation, mounted on an air spindle 30 which is movable alongthe axis of rotation of the grinding stone, and having a cylindricalportion and a disk-shaped portion; an electrode 21 provided with apredetermined distance from a ring-shaped working end surface of thecylindrical portion of the grinding stone 20; a DC power 22 connected tothe electrode 21 and the air spindle 30 such that the electrode and thegrinding stone serve as a cathode and an anode, respectively; means 23for supplying, between the electrode and the stone, a grinding solutionwith silica fine particles (colloidal silica) 24 dispersed therein; anda sample table 26 opposed to the ring-shaped working end surface anddisposed to mount the object 25 thereon.

[0004] While in the above grinding device, the grinding solution issupplied between the electrode 21 and the grinding stone 20, negativeand positive voltages are applied to the electrode 21 and the grindingstone 20 from the DC power 22, respectively, thereby electricallyattaching, to the surface of the grinding stone, silica fine particleswhich have been charged with negative electricity. Thus, a silicafine-particle layer is formed on the grinding stone surface, as a resultof the electrophoresis phenomenon. In this state, the grinding stone 20is gradually moved along the axis of rotation, and the silicafine-particle layer is brought into contact with the to-be-workedsurface of the object. At the same time, the grinding stone 20 isrotated about the rotation axis to thereby make silica fine particlesserve as a grinding blade for grinding the object. As a result, theobject surface is polished into a mirror surface with little damage.

[0005] The above-described grinding method is effective in a case wherethe to-be-worked surface of the object has beforehand a certain shape(which is not a final surface shape or a surface of a mirror state), andis polished into a mirror surface by slightly removing materialtherefrom using silica fine particles. For example, the method iseffective where only a very thin or small portion of a material has tobe ground as in the case of a semiconductor wafer, and it is necessaryto minimize the degree of deformation inside the worked material.

[0006] However, since in the above-described prior case, the electricalforce for holding silica fine particles on the grinding stone is muchsmaller than the force for grinding the material, the fine particleswill fall from the grinding stone if deep cuts are formed in thegrinding stone to create a great working force.

[0007] In light of this, it is necessary to set the depth of cuts in thegrinding stone at an extremely low value of several microns or less, inorder to prevent falling of silica fine particles from the stone and toeffectively use them as grinding particles.

[0008] Therefore, grinders having cuts with a depth of several micronsor less are not effective in deeply grinding a workpiece, for example,to generate an optical element such as a lens from a glass blank (anoptical glass workpiece). Since the cutting amount of the grinders isextremely small, efficient grinding cannot be performed, and hence anextremely long cutting time is required. This being so, it is necessaryin the prior technique to beforehand prepare a material which has itsto-be-worked surface ground into as close a shape as possible to thefinal shape, using another polishing or grinding device. Thus, lots oftime is necessary for preparation of such a half product or forgeneration of a mirror surface from the workpiece or material.

BRIEF SUMMARY OF THE INVENTION

[0009] It is the object of the invention to provide a grinding methodfor simultaneously performing shape generation and mirror surfacegrinding of an optical glass-material, and a glass lens worked by thegrinding method.

[0010] Additional object and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobject and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outin the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0011] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0012] FIGS. 1 to 3 are views, schematically showing a grinding devicefor executing a grinding method according to a first embodiment of theinvention, in which

[0013]FIG. 1 shows a state before grinding,

[0014]FIG. 2 a state in which an optical glass material is made toapproach a grinding stone so that it can be ground, and

[0015]FIG. 3 a state in which the material is being ground;

[0016]FIG. 4 is a schematic view similar to FIG. 3, showing a grindingdevice for executing a grinding method according to a second embodimentof the invention;

[0017]FIG. 5 is a sectional view, showing a modification of the grindingstone employed in the second embodiment;

[0018] FIGS. 6 to 8 are views useful in explaining grinding methodsaccording to third and seventh embodiments, in which

[0019]FIG. 6 shows a state before grinding,

[0020]FIG. 7 a state assumed while an optical glass workpiece is beingground by the grinding stone, and FIG. 8 the final step of grinding;

[0021]FIGS. 9A and 9B are graphs, showing measurement results obtainedby measuring the surface roughnesses of objects ground with the grindingmethod of the third embodiment and a usual grinding method;

[0022]FIG. 10 is a schematic view, useful in explaining a grindingmethod according to a fourth embodiment of the invention;

[0023] FIGS. 11 to 13 are views, useful in explaining a grinding methodaccording to a fifth embodiment of the invention, in which

[0024]FIG. 11 shows a state before grinding,

[0025]FIG. 12 a state assumed while an optical glass material is beingground by the grinding stone, and

[0026]FIG. 13 the final step of grinding;

[0027]FIG. 14 is a view, useful in explaining a grinding methodaccording to a sixth embodiment of the invention;

[0028]FIG. 15 is a view, useful in explaining the grinding methodaccording to the seventh embodiment, together with FIGS. 6 to 8;

[0029]FIG. 16 is a view, showing a fine polishing trace pattern of thesurface of a lens worked by the grinding method of the third embodiment;and

[0030]FIG. 17 is a view, useful in explaining a conventional grindingmethod using the electrophoresis phenomenon.

DETAILED DESCRIPTION OF THE INVENTION

[0031] A grinding method according to a first embodiment of theinvention will be described with reference to FIGS. 1 to 3 in which themethod is applied to a flat lens as an optical element.

[0032] As is shown in FIG. 1, a to-be-worked disk-shaped optical glassmaterial or workpiece 1 is held by a vacuum force on a chuck 2 which iscoaxially attached to an end of the rotary shaft of a driving unit (notshown) for rotating the material 1. The optical glass material 1 can berotated by the chuck 2 about the central axis (W axis) of the rotaryshaft of the chuck.

[0033] A grinding stone 3 is disposed obliquely above the optical glassmaterial 1 for grinding the material. The grinding stone 3 is supportedby known means on one end of a conductive rotary shaft 4 such that thecentral axis (T axis) of the rotary shaft 4 is parallel to the W axis.The other end of the rotary shaft 4 is connected to the aforementionedgrinding stone driving unit. Concerning the optical-glass material 1 andthe grinding stone 3 located obliquely above it, the T axis is notaligned with the W axis and the diameters of the grinding stone 3 andthe workpiece 1 are set so that a side face portion 3 a of the stone 3and a side face portion 1 c of the material 1 will not interfere witheach other, before the stone works the material, even when the grindingstone 3 is lowered along the T axis.

[0034] The grinding stone driving unit connects the grinding stone 3 toa two-directionally and linearly advancing unit (not shown) such thatthe grinding stone 3 can move along the T-axis direction and a directionperpendicular thereto.

[0035] The grinding stone 3 comprises a disk-shaped portion and acylindrical portion formed integral with the disk-shaped portion andconcentrically projecting therefrom. In other words, the grinding stone3 is cup-shaped. The stone 3 is formed by fixing grinding particles suchas diamond with a conductive bonding material (e.g. bronze, nickel orcast iron), and electrically connected to the rotary shaft 4.

[0036] The side face portion 3 a of the grinding stone 3 functions as ashape-generating face, which cuts and removes an unnecessary portion ofthe optical glass material 1 from its side face portion 1 c when thegrinding stone 3 rotates and moves to the optical glass material 1 inthe direction perpendicular to the T axis, thereby grinding the material1 into a desired shape (final shape).

[0037] The front or lower end face 3 b of the cylindrical portion of thegrinding stone 3 is a ring-shaped flat face, which is perpendicular tothe T axis and has its center aligned with the T axis. The front faceportion 3 b functions as a polishing face for polishing the surface ofthe material shaped by the side face portion (shape-forming face) 3 a.The polishing by the front face portion 3 b is performed simultaneouswith the shaping by the side face portion 3 a, using silica fineparticles (which will be described later).

[0038] A nozzle 6 is located below the grinding stone 3 in a positionopposite to the optical glass material 1 with respect to the T axis, inorder to apply, to the optical glass material 1 and the grinding stone3, a polishing solution 5 which contains silica fine particlespre-charged with negative electricity (colloidal silica with an averageparticle diameter of φ 10 nm). An electrode 7 is provided in thevicinity of the discharge port of the nozzle 6 such that it is opposedto part of the front face portion 3 b of the grinding stone 3 with apredetermined space therebetween. The electrode 7 is connected to thecathode of a DC power 8, and the anode of the power 8 is connected tothe rotary shaft 4.

[0039] The grinding method using the above-described grinding devicewill be described with reference to FIGS. 1 to 3.

[0040] First, the optical glass material 1 is held on the chuck 2, andthe workpiece 1 with the chuck 2 and the grinding stone 3 are arrangedas shown in FIG. 1. Then, the material 1 and the grinding stone 3 arerotated about the W axis and the T axis by the object driving unit andthe grinding stone driving unit, respectively. At the same time, thepolishing solution 5 is discharged from the nozzle 6 onto the grindingstone 3, the optical glass material 1 and the electrode 7, and the DCpower 8 applies a negative voltage to the electrode 7 and a positivevoltage to the grinding stone 3 via the rotary shaft 4.

[0041] Subsequently, as shown in FIG. 2, the grinding stone 3 is loweredalong the T axis and situated in a position near a side portion of theoptical glass material 1. In this position, the front face portion 3 bof the grinding stone 3 vertically reaches a final shape surface 1 a ofthe material 1 (i.e. the surface obtained when the material 1 is cut byan amount of H), and the lower end (outer peripheral edge) of the frontface portion 3 b does not contact the material 1 (i.e. the lower enddoes not interfere with the upper surface and the side face portion 1 cof the material 1). The electrode 7 and the nozzle 6 are loweredtogether with the grinding stone 3. To enable the movement of theelectrode 7 and the nozzle 6 with the grinding stone 3, they may bemechanically connected to each other by means of a common member, ortheir movement may be synchronized by a driving mechanism different fromthat of the grinding stone 3.

[0042] Silica fine particles jetted from the nozzle 6 and charged withnegative electricity are electrically attracted by and attached to thegrinding stone 3 to which positive voltage is applied, as a result ofthe so-called electrophoresis phenomenon. The grinding stone 3 of thisstate is shifted toward the W axis, i.e. to the right in FIG. 2. Then,as shown in FIG. 3, the side face portion 3 a is brought into contactwith the side face portion 1 c of the material 1, and starts to cut itby the cutting amount of H, thereby shaping the material 1 using theside face portion 3 a as a generating work surface. At the same time,the front face portion 3 b is passed along the final shape surface 1 agenerated by the side face portion 3 a (which means the so-called creepfeed grinding). Since the grinding for shaping the optical glassmaterial 1 is performed by the side face portion 3 a, a very strongergrinding force (working force), i.e. a stronger force for removing theunnecessary portion (the portion to be removed by the cutting amount ofH) of the material 1, occurs during grinding at the side face portion 3a than at the front face portion 3 b. Accordingly, the silica fineparticles are not-liable to electrically attach to the side face portion3 a. However, since the grinding stone 3 is of a multi-blade structurewhich includes lots of grinding particles, and there are alwaysprojecting grinding particles on the grinding stone 3, the optical glassmaterial 1 can sufficiently be shaped by only the projecting particles.This means that even if many of silica fine particles fall from the sideface portion 3 a, it will not greatly influence the material shaping. Onthe other hand, silica fine particles are more liable to attach to thefront face portion 3 b during the working than to the side face portion3 a. This is because on the front face portion 3 b, the difference inheight between the grinding particles and the bonding material issufficient as a clearance which is required for holding the fineparticles (such a clearance as enables electrical attraction of the fineparticles enough to make it difficult for them to fall), and alsobecause the front face portion 3 b does not cut the material, i.e. thecutting amount is zero, and hence it requires only a small workingforce.

[0043] Where lots of silica fine particles attach to the front faceportion 3 b, the clearance between the grinding particles and thebonding material is filled with them, and therefore the total projectionof the grinding particles on the front face portion 3 b appears low.Accordingly, when the front face portion 3 b passes along the finalshape surface 1 a, it polishes the surface 1 a into a mirror surface,using both the grinding particles whose total projection appears low,and the silica fine particles attaching to the front face portion 3 b.

[0044] In other words, the front face portion 3 b functions as apolishing face, and the silica fine particles attaching thereto are usedto perform mirror-surface grinding of a form-shaped material. Althoughduring grinding, lots of silica fine particles electrically attaching tothe front face portion 3 b sequentially fall because of the grindingforce, negative-voltage-charged silica fine particles are sequentiallycreated from the polishing solution 5 which is always supplied by thenozzle 6, and attach to the front face portion 3 b of the grinding stone3. As a result, there is no degradation of polishing performance due tofall of silica fine particles. Further, since the silica fine particlesattaching to the grinding stone 3 absorb shock which occurs duringgrinding, the rotation of the grinding stone 3 is stabilized, whichprevents that run-out of the grinding stone 3 or that excessive cuttingof the optical glass material 1 by the grinding particles, which maywell cause a defect such as a crack in the material 1.

[0045] After the grinding stone 3 further moves and the side faceportion 3 a reaches the W axis, the grinding stone 3 is moved upwardalong the T axis to separate from the optical glass material 1. Then,the supply of the polishing solution 5, the voltage application by thepower 8, and the rotation of the grinding stone 3 and the material 1 arestopped, and the resultant flat lens is taken from the chuck 2. A flatlens with its both opposite sides polished can be obtained by placingthe one-side polished flat lens on the chuck 2 with its reverse surfacedirected upward, and repeating a working process as above.

[0046] Although in the above embodiment, the grinding stone 3 is movedto the optical glass material 1 to grind it, the same working can beperformed by shifting the optical glass material 1 in a directionperpendicular to the W axis with the grinding stone 3 kept rotate in afixed position, or by causing both the grinding stone 3 and the material1 to approach each other.

[0047] In the above embodiment, shaping and polishing (mirror surfacegrinding) of a material can be performed simultaneously using a generalgrinding stone. Accordingly, the time required for the shaping andpolishing can be significantly shortened as compared with theconventional case.

[0048] Further, since silica fine particles contained in the polishingmaterial 5 absorb shock which occurs during grinding, the rotation ofthe grinding stone 3 is stabilized. Therefore, run-out of the grindingstone 3 is prevented, thereby avoiding the excessive cutting of theoptical glass material 1 by the grinding particles which may well causea defect such as a crack in the material 1.

[0049] Although in the embodiment, colloidal silica is used as a fineparticle substance contained in the polishing material 5, the sameeffect can be obtained if colloidal cerium is used. Moreover, it mayeasy to understand that other fine particles known in this technicalfield may be used.

[0050] Moreover, although in the embodiment, both the grinding stone 3and the optical glass material 1 are rotated, it may be modified suchthat one of them is rotated in light of whether or not the material 1 iseasy to grind, the desired surface configuration of the material 1, orwhether or not a to-be-cut portion of the material 1 is large. In thiscase, it is necessary to control the grinding stone 3 so that the frontface portion 3 b will pass the overall area of the final shape surface 1a (the to-be-polished surface of the optical glass material 1).

[0051] Furthermore, although in the embodiment, a flat lens is ground,an optical element of any other shape, such as a prism, may be ground.

[0052] Referring then to FIG. 4, a grinding method according to a-secondembodiment will be described.

[0053]FIG. 4 shows a state where the side face portion 9 a of acup-shaped grinding stone 9 cuts the optical glass material 1 from itsperiphery 1 c by a cutting amount of H in a direction perpendicular tothe T axis. Both the grinding stone 9 and the optical glass material 1are rotated.

[0054] The front face portion 9 b of the grinding stone 9 is inclinedsuch that when its outer peripheral edge contacts a to-be-polished flatsurface of the optical glass material 1, it slants gradually away fromthe material 1 in a direction toward the T axis. In other words, thefront face portion 9 b is inclined such that its edge becomes highertoward the T axis with respect to the plane perpendicular to the T axis;that is, the front face portion 9 b is tapered from the outer peripheraledge to the inner peripheral edge. The other structural elements of thesecond embodiment are similar to those of the first embodiment, andhence no detailed description is given thereof. Further, the secondembodiment performs grinding in the same procedure as in the firstembodiment.

[0055] Since in the second embodiment, the front face portion 9 b of thegrinding stone 9 is tapered, part of the front face portion iscompletely out of contact with the final shape surface (to-be-polishedsurface) 1 a of the optical glass material 1 during grinding (in theFIG. 4 state). On the non-contact portion, grinding particles projectingfrom the bonding material are out of contact with the optical glassmaterial 1, and therefore only silica fine particles attaching to partof the front face portion 9 b (or silica particles attaching to thefront face portion 9 b and forming a lamination) are brought intocontact with the optical glass material 1. Accordingly, the amount ofpolishing by silica fine particles increases, which means that higherquality mirror surface grinding is performed in the second embodimentthan in the first embodiment.

[0056] The front face portion 9 b of the grinding stone 9 can have ashape other than the above-described one. For example, as is shown inFIG. 5, the front face portion 9 a may have a plurality (two in FIG. 5)of annular surfaces which extend perpendicular to the T axis and shiftsalong the T axis. In the FIG. 5 case, a cup-shaped grinding stone 10 hasa front face portion 10 b stepped along the T axis and consisting of anouter annular flat face 10 c and an inner annular flat face 10 d. Thedifference in height-between the flat faces 10 c and 10 d is set at avalue not higher than the height of silica fine particles to be adheredto the grinding stone 10.

[0057] In the grinding stone 10, at the outer flat face 10 c, grindingparticles projecting from the bonding material are put into contact withthe optical glass material 1, which means that the outer flat face 10 chas a function similar to the front face portion 3 b (in FIG. 1) of thegrinding stone 3 employed in the first embodiment. On the other hand, atthe inner flat face 10 d, grinding particles projecting from the bondingmaterial are out of contact with the optical glass material 1, whichmeans that the inner flat face 10 d has a function similar to thenon-contact portion employed in the second embodiment. Since in thegrinding stone 10, stress concentration at the outer edge of the frontface portion 10 b, i.e. between the outer flat face 10 c and the sideface portion 10 a, is reduced to thereby suppress the occurrence ofchipping off of the grinding stone and enable stable grinding.

[0058] Referring then to FIGS. 6, 9A and 9B, application of a grindingmethod according to a third embodiment to grinding of a spherical lenswill be described.

[0059] As is shown in FIG. 6, the rotary shaft (W axis) W of the chuck 2is substantially perpendicular to the rotary shaft (T axis) T of therotary shaft 4 which supports the grinding stone 9. The axis of anoptical glass material 11 to be ground is identical to the W axis, andthe optical glass material 11 is held by the chuck 2 such that it canrotate about the W axis. The chuck 2 is attached to the rotary shaft ofa driving unit (not shown) for rotating a to-be-ground object, and thedriving unit is incorporated in an object shifting unit (not shown) suchthat it can move along the W axis.

[0060] A cup-shaped grinding stone 9 is provided on a lateral side ofthe optical glass material 11. Since the grinding stone 9 has the samestructure as that employed in the second embodiment, no description isgiven thereof. The grinding stone 9 is held by the conductive rotaryshaft 4 such that it can rotate about the T axis as an axis of rotation,which coincides with the axis of the front face portion 9 b and on whichaxis the center-of-curvature O of a sphere into part of which theoptical glass material 11 is cut exists.

[0061] The rotary shaft 4 is attached to a grinding stone driving unit(not shown), and the grinding stone driving unit is incorporated in agrinding stone shifting unit (not shown) such that the grinding stone 9can move along the T axis. The grinding stone shifting unit isincorporated in a driving mechanism (not shown) such that it can revolveor swing about the center-of-curvature O. This driving mechanism has anozzle 6 and an electrode 7, which are similar to those in the first andsecond embodiments and can follow the rotation of the grinding stone 9(angular movement from a state shown in FIG. 6 in which the stone issubstantially perpendicular to the optical glass material 11, to a statein which the angle therebetween is reduced), with a relativerelationship to the grinding stone 9 kept. A specific state in which thenozzle and the electrode 7 are attached is not shown. The other elementshave the same structures as in the first and second embodiments, andtherefore no description is given thereof.

[0062] Referring to FIGS. 6-8, a grinding method employed in theabove-described grinding device will be described.

[0063] First, the T-axial position of the grinding stone 9 is set sothat a to-be-generated spherical shape of a workpiece 11 will coincidewith the locus of the front face portion 9 b of the grinding stone 9which is obtained when the grinding stone 9 is rotated. Specifically, asshown in FIG. 6, the grinding stone 9 is moved along the T axis by thestone shifting unit and positioned so that when the grinding stone 9 isrevolved by the driving unit, the locus of the front face portion 9 b inthe optical glass material 11 will follow a circular arc which has thesame curvature as a to-be-generated spherical shape. In other words, thegrinding stone 9 is positioned so that the distance between thecenter-of-rotation O and the portion of the optical glass material 11along which the front face portion 9 b passes will coincide with theradius-ofcurvature 12 of the to-be-generated spherical shape.

[0064] Subsequently, the optical glass material 11 is set on the chuck 2of the object driving unit, and the W-axial position of the material 11is determined using the object shifting unit so that the locus of thefront face portion 9 b in the optical glass material 11 will follow acircular arc having the same curvature as the to-be-generated sphericalshape, thereby determining the amount of cutting which starts from theperiphery of the material 11.

[0065] After positioning of the grinding stone 9 and the optical glassmaterial 11, the material 11 is rotated about the W axis by the objectdriving unit, and the grinding stone 9 is rotated about the T axis bythe stone driving unit. At the same time, a polishing solution 5 whichcontains silica particles (colloidal silica) with negative charge isapplied between the grinding stone 9 and the electrode 7 from the nozzle6, and a negative voltage is applied from the DC power 8 to theelectrode 7, and a positive voltage from the DC power 8 to the grindingstone 9 via the rotary shaft 4. The silica particles with negativecharge are electrically attracted, as a result of the so-calledelectrophoresis, by the grinding stone 9 with the positive voltage, andelectrically attached thereto.

[0066] Thereafter, the edge of the side face portion 9 a (i.e. the outeredge of the front face portion 9 b) of the grinding stone 9 is revolvedby the driving unit about the center O of the to-be-generated sphericalshape, so that a spherical shape with a radius-of-curvature 12 can bedrawn, thereby starting arcuate cutting θ of the optical glass material11 from its periphery, using the side face portion 9 a as ashape-generating surface, as is shown in FIG. 7.

[0067] While the arcuate cutting θ is continued, a final spherical shapeis generated by the edge of the side face portion 9 a, and at the sametime, the front face portion 9 b is passed along the final sphericalshape generated by the edge of the side face portion 9 a (so-calledcreep feed grinding is performed). Since in this grinding, the side faceportion 9 a receives a very strong grinding force for generating a shape(removing an unnecessary portion of the optical glass material), most ofsilica fine particles attached thereto will fall and be hard toreattach. However, the grinding stone 9 is of a multi-blade structurewhich includes lots of grinding particles, and hence there always existgrinding particles projecting from the grinding stone 9. These grindingparticles can sufficiently shape the side face portion 9 a. Thus, evenwhen most of silica fine particles fall from the side face portion 9 a,shape generation can be performed without any trouble.

[0068] On the other hand, during grinding, silica fine particles attachmore easily to the front face portion 9 b than to the side face portion9 a. This is because on the front face portion 9 b, the difference inheight between the grinding particles and the bond material issufficient to define a space for holding silica fine particles(sufficient to keep them electrically) therein, and because the frontface portion 9 b does not perform cutting and therefore use a largegrinding force.

[0069] When lots of silica fine particles attach to the front faceportion 9 b, they are filled between the grinding particles and bondmaterial, and therefore the total projection of grinding particles onthe front face portion 9 b appears low. Accordingly, when the front faceportion 9 b passes along the material of the final spherical shape, itpolishes the material into a mirror surface, using both the grindingparticles whose total projection appears low, and the silica fineparticles attaching to the front face portion 9 b.

[0070] Although during grinding, lots of silica fine particleselectrically attaching to the front face portion 9 b sequentially fallbecause of the grinding force, they are-sequentially created from thepolishing solution 5 which is always supplied by the nozzle 6, andattach to the front face portion 9 b. As a result, there is nodegradation of polishing performance due to fall of silica fineparticles. Further, since the silica fine particles attaching to thegrinding stone 9 absorb shock which occurs during grinding, the rotationof the grinding stone 9 is stabilized, which prevents that run-out ofthe grinding stone 9 or that excessive cutting of the optical glassmaterial 11 by the grinding particles, which may well cause a defectsuch as a crack in the material 11.

[0071] When the arcuate cutting θ is continued, and the edge of thefront face portion 9 b which contacts the optical glass material 11 hasreached the W axis as shown in FIG. 8, the cutting is stopped.

[0072] After the termination of the arcuate cutting θ, the grindingstone 9 is moved upward along the T axis to be separated from theoptical glass material 11, and is revolved by the driving unit to theinitial position, i.e. the position shown in FIG. 6. At the same time,the supply of the polishing material 5 through the nozzle 6, the voltageapplication by the DC power 8, and the rotation of the grinding stone 9and the optical glass material 11 are stopped, and a flat convex lens asa resultant product is taken from the chuck 2.

[0073] In the above embodiment, arcuate cutting θ of the optical glassmaterial is performed by revolving the grinding stone 9 about thecenter-of-curvature O, to form a spherical shape. However, it can alsobe done by revolving the optical glass material 11 in a directionopposite to the θ-directional rotation of the grinding stone 9, afterpositioning the grinding stone 9 and the material 11 along the T axisand the W axis, respectively, and fixing the grinding stone 9 inposition.

[0074] A convex lens with its both opposite sides shaped as convexsurfaces can be obtained by placing the one-side worked lens on thechuck 2 with its reverse surface directed upward, and repeating aprocess as above.

[0075] As described above, spherical shape generation and mirror surfacegrinding can be simultaneously performed simply by rotating the grindingstone 9 about the center-of-curvature O of a to-be-generated sphericalshape, i.e. by simple angular movement i.e. one-axis movement of thestone 9. The other advantages of the second embodiment are similar tothose of the first embodiment.

[0076] In the third embodiment, the front face portion 9 b has a taperedsurface, i.e. has a surface shape differing from a to-be-generatedspherical shape. If, however, the front face portion 9 b is madebeforehand to have the radius-of-curvature 12 of the to-be-generatedspherical shape, it can shape the optical glass material 11 at a highersurface accuracy or shape accuracy. Further, a grinding stone may beused which has a flat front face portion as employed in the firstembodiment, or has a front face portion with an axial semi-circularsection (which means that the edge of the cup-shaped grinding stone hasa semi-circular section). In addition, although the grinding stone 9 issituated in a position in which the T axis intersects the W axis in FIG.6 (showing a state before grinding), it is not always necessary to makethe T and W axes intersect each other. It suffices if the side faceportion 9 a of the grinding stone 9 is out of contact with the opticalglass material 11.

[0077] A case where the grinding method according to the thirdembodiment is applied to actual grinding will be described.

[0078] In this case, FPL53 was used as the optical glass material 11,and SD800N100MF41 produced by Shin-Nissan Diamond Corporation, in which# 800 diamond grinding particles are fixed by a metallic bond, was usedas the grinding stone 9. A solution which contains a 6 wt % colloidalsilica polishing material with a particle diameter of 30-80 Å was usedas the polishing solution 5. The distance between the grinding stone 9and the electrode 7 was set at 1-2 mm, and a voltage of 40V was appliedbetween the electrode 7 and the grinding stone 9.

[0079] Under the above-described conditions and in the state shown inFIG. 6, the grinding stone 9 and the optical glass material 11 wererotated at 7000 rpm, the polishing solution 5 was applied between thegrinding stone 9 and the electrode 7, and a voltage of 40V was appliedbetween the electrode 7 and the grinding stone 9. This state was keptfor 20 minutes, thereby electrically attaching silica fine particles tothe grinding stone 9. Thereafter, as shown in FIG. 7, the supply of thepolishing solution 5 and the application of the voltage were continued,while the grinding stone 9 was advanced into the optical glass material11 at a circumferential speed of 6 mm/min. (where the W-axial depth ofthe material 11 by which it should be cut is set at 0.1 mm). Theremaining portion of the procedure is the same as the third embodiment.

[0080] The comparison was performed of a surface resulting from theabove-described grinding method, and a surface (a comparative) resultingfrom another case using a grinding method similar to the above exceptthat no voltage was applied between the electrode 7 and the grindingstone 9 (hereinafter referred to as “usual grinding method”). Actually,pictures of the resultant surfaces, which were obtained by the Nomarskimicroscope set at a power of 100, were compared. As a result, abrasionsdue to diamond grinding particles contained in the grinding stone wereobserved in the comparative, whereas no such abrasions were found in thesurface obtained by the grinding method of the invention. This meansthat the abrasions were removed during polishing by silica fineparticles. Further, it was recognized from the picture of the surfaceobtained by the invention that striped traces from polishing werelocally formed in place of the abrasions.

[0081] Then, the roughness of the surface resulting from the thirdembodiment and that resulting from the usual grinding method weremeasured for comparison.

[0082]FIG. 9A shows the measurement results of the surface obtained bythe third embodiment, and FIG. 9B the measurement results of the surfaceobtained by the usual grinding method.

[0083] In each of FIGS. 9A and 9B, the abscissa indicates the measuredlength (one division: 50 μm), and the ordinate the surface roughness(one division: 0.1 μm). In the case of the usual grinding method, theaverage roughness Rave and the maximum roughness Rmax were 0.018 μm and2 μm, respectively, as shown in FIG. 9B. On the other hand, in the caseof the third embodiment, Rave and Rmax were 0.005 μm and 0.046 μm,respectively, as shown in FIG. 9A.

[0084] It was confirmed also from the surface roughness measurementresults that the grinding method of the embodiment can provide a surfacecloser to a mirror surface than the usual grinding method. Moreover,when the overall area of the glass lens surface processed in theembodiment was observed using the Nomarski microscope or an interatomicforce microscope, there were traces resulting from polishing by silicafine particles.

[0085] When the surface processed in the embodiment was observed usingthe Nomarski microscope set at a power of about 1000, extremely finepolishing traces, which seemed to indicate relative movements of thegrinding stone 9 and the optical glass material 11, were found. Further,when the surface was observed using the interatomic force microscope, itwas detected that the depth of the polishing traces ranged from 1 nm to10 nm. In particular, a polishing trace was especially clearly observed,which was similar to a locus and obtained when the process wascompleted, i.e. when the arcuate cutting θ by the grinding stone 9 wascompleted and the front face portion 9 b coincides with the W axis.

[0086] The thus-observed polishing trace is shown in FIG. 16. In thecase of the embodiment, a polishing trace 19 like lots of “flowerpetals” was observed as shown in FIG. 16. Since the polishing trace 19is a group of striped traces caused by polishing by silica fineparticles, it is very fine and characterized, in particular, in that itis formed by silica fine particles electrically attached to the grindingstone 9, and hence has a regular geometrical pattern, which differs froman irregular polishing pattern observed in the conventional polishingusing isolated grinding particles. In other words, the polishing traceindicates a locus formed as a result of movements of the grinding stone9 and the optical glass material 11.

[0087] Although in the embodiment, the polishing trace 19 shown in FIG.16 was observed, it cannot always be found since the resultant tracedepends upon the manner of movement. It is a matter of course that thetrace changes when a different cutting method is employed. In additionto this, the polishing trace 19 will change only if the speed of angularcutting or the rotational speed of the optical glass material ischanged. However, so long as the polishing trace is based on polishingperformed by fine particles attached to the grinding stone due to theelectrophoresis phenomenon, it always shows a regular though varyingpattern.

[0088] Depending upon the quality level of a glass lens, for example, inthe case of a lens for use in a semiconductor exposure device, it may benecessary to further polish the regular polishing trace into anirregular one by finishing polishing such as known pitch polishing whichuses an isolated grinding stone. Since, however, the fine polishingtrace 19 formed by silica fine particles has a depth of 10 nm or less,the glass lens formed by the invention can show sufficient opticalproperties for various purposes, and hence does not require the step oftroublesome finishing polishing as employed in the conventional case.Accordingly, a glass lens can be produced in a short time at low cost.

[0089] A fourth embodiment of the invention will be described withreference to FIG. 10.

[0090] The fourth embodiment is characterized in that cutting of theoptical glass material 11 into a spherical shape with aradius-of-curvature 12 is performed in two stages. Since the basicstructure of a grinding device used in this embodiment is similar tothat in the third embodiment, no detail explanation will be giventhereof.

[0091] First, as shown in FIG. 10, the W-axial positioning of theoptical glass material 11 is performed in the same manner as in thethird embodiment, and then the T axis of the grinding stone 9 isinclined with respect to the W axis, thereby causing the grinding stone9 to standby at the front face portion side of the optical glassmaterial 11.

[0092] The inclination of the T axis is set to a value at which thefront face portion 9 b can interfere with the optical glass material 11when it is moved to the material.

[0093] Then, the optical glass material 11 is rotated about the W axisby a to-be-processed object driving unit (not shown), and the grindingstone 9 is rotated about the T axis by a grinding stone driving unit(not shown). At the same time, the polishing solution 5 which containssilica fine particles (colloidal silica; the average particle diameter:φ 10 nm) with negative charge is supplied between the grinding stone 9and the electrode 7, while a negative voltage is applied from the DCpower 8 to the electrode 7, and a positive voltage from the same powerto the grinding stone 9 via the rotary shaft 4. The silica fineparticles with negative charge are electrically attracted, as a resultof the so-called electrophoresis, by the grinding stone 9 with thepositive voltage, and electrically attached thereto.

[0094] Subsequently, the grinding stone 9 is advanced along the T axis,thereby starting linear cutting R of a corner portion of the opticalglass material 11. The first-stage cutting is performed by the frontface portion 9 b. Since at this time, the front face portion 9 bfunctions as a shape generating face unlike the third embodiment, alarge force acts thereon, and hence most of silica fine particlesattached thereto will fall. However, it suffices, in the first cuttingstage, if grinding particles projecting from the front face portion 9 bcut the optical glass material 11 in accordance with the conventionalcutting method. Therefore, no problems will arise. The linear cutting Ris continued, and finished when the front face portion 9 b has reached aline which is defined by the radius-of-curvature 12 of a to-be-generatedspherical surface.

[0095] Thereafter, as in the third embodiment, arcuate cutting θ of theoptical glass material 11 is performed by revolving the grinding stone 9using its driving unit, to form the spherical surface. In other words,the second-stage cutting is performed by the side face portion 9 a. Inthis stage, shaping of the spherical surface and polishing of thesurface of the shape are simultaneously performed as in the thirdembodiment. Since thus, the portion cut in the first stage is polishedby silica fine particles attached to the front face portion 9 b in thesecond stage, a similar process to the third embodiment is performed.

[0096] Since in the fourth embodiment, a force to be applied to thegrinding stone 9 at the start of cutting can be reduced by bringing thegrinding stone 9 into contact with the optical glass material 11 by thelinear cutting R in the first stage, peripheral chipping of the material11 (cracking of glass like a shell) can be substantially avoided.Moreover, although a spherical surface is generated by rotating thegrinding stone 9 and thereby performing arcuate cutting θ of the opticalglass material 11, arcuate cutting θ can also be performed so that thematerial 11 has the same spherical surface, by rotating the opticalglass material 11 in a direction opposite to the θ-direction in whichthe grinding stone 9 is rotated, after performing the linear cutting Rand then fixing the grinding stone 9 in position.

[0097] Accordingly, the fourth embodiment can provide a product (forexample, a glass lens) with excellent outward appearance and quality.

[0098] Although as in the third embodiment, a fine polishing trace of aregular pattern was observed on the surface of the product resultingfrom the fourth embodiment, its optical properties were sufficient forvarious purposes. Further, since in the first stage, T-axial bending ofthe grinding stone 9 due to the radial force can be suppressed, aproduct of a high shape accuracy can be obtained. The other advantagesof the fourth embodiment are similar to those of the third one.

[0099] Referring then to FIGS. 11 to 13, a grinding method according toa fifth embodiment will be described.

[0100] A grinding device employed in the fifth embodiment is similar tothose used in the third and fourth embodiments, except that it isequipped with an angle setting mechanism (not shown) for adjusting onlythe angle of the T axis with respect to the W axis.

[0101] The grinding device may have the same structure as the knowncurve generator. The grinding method according to the fifth embodimentincludes two stages. In the first stage, the optical glass material 11is not rotated, and the grinding stone 9, whose inclination is set at acertain value, is rotated and at the same time linearly moved to cut thestationary material 11. In the second stage, the surface of the opticalglass material 11 is ground while it is rotated, using the rotating andinclined grinding stone 9.

[0102] Specifically, the grinding is performed as follows:

[0103] First, the inclination angle of the T axis to the W axis isobtained. The inclination angle is obtained by a method similar to themethod employed in the known curve generator for determining the swivelangle. It is determined from the shape of the grinding stone 9 and theshape of a to-be-generated spherical surface, and more particularly isdetermined so that the spherical shape can be generated simply byrotating the optical glass material 11 with the grinding stone 9 kept incontact with the material 11. After determination of the inclinationangle, the rotary shaft 4 of the grinding stone 9 is inclined by theangle setting mechanism and kept inclined.

[0104] Subsequently, the grinding stone 9 is rotated about the T axis ofthe rotary shaft 4, and at the same time, the polishing solution 5 whichcontains silica particles with negative charge is applied between thegrinding stone 9 and the electrode 7 from the nozzle 6, and a negativevoltage is applied from the DC power 8 to the electrode 7, and apositive voltage from the DC power 8 to the grinding stone 9 via therotary shaft 4. The silica particles with negative charge areelectrically attracted, as a result of the so-called electrophoresis, bythe grinding stone 9 with the positive voltage, and electricallyattached thereto.

[0105] Then, the grinding stone 9 is linearly moved along the T axis,and starts linear cutting R using the front face portion 9 b as a shapegenerating face (first-stage cutting). During the linear cutting, alarge force acts on the front face portion 9 b, and hence most of silicafine particles attached thereto will fall. However, it suffices, in thefirst cutting stage, if grinding particles projecting from the frontface portion 9 b cut the optical glass material 11 in accordance withthe conventional cutting method. Therefore, no problems will arise.

[0106] The linear cutting R is continued, and finished when the frontface portion 9 b has reached a line which is defined by theradius-of-curvature 12 of a to-be-generated spherical surface. Since atthis time, the optical glass material 11 is not rotated, the grindingstone 9 sticks into the material 11.

[0107] Thereafter, while the supply of the polishing material 5 iscontinued, the optical glass material 11 is rotated about the W axis,thereby making the side face portion 9 a cut into the material 11. Sincethe rotational speed of the material 11 also functions as the cuttingspeed of the grinding stone 9, it set lower than that employed in thethird embodiment.

[0108] With the rotation of the optical glass material 11, the side faceportion 9 a of the grinding stone 9 stucks to the material advances init. When the optical glass material 11 is rotated one full turn, cuttingof the material into a spherical shape is completed as shown in FIG. 13.Then, the resultant flat convex lens is taken from the chuck 2. When theoptical glass material 11 has been cut into the spherical shape, thefront face portion 9 b of the grinding stone 9 intersects the W axis.Since no linear cutting R is performed by the grinding stone 9 when theside face portion 9 a removes the unnecessary portion of the opticalglass material 11 by rotating the material about the W axis, almost nogrinding force is exerted on the front face portion 9 b. Accordingly, asin the third embodiment, the silica fine particles attached to the frontface portion 9 b of the grinding stone 9 polish the to-be-processedsurface. In other words, the front face portion 9 b functions as apolishing face.

[0109] The fifth embodiment can perform cutting, like the conventionalcurve generator, without the driving unit for revolving the grindingstone 9 employed in the third and fourth embodiments. In addition,although in the fifth embodiment, the grinding stone 9 is linearly movedalong the T axis, thereby performing linear cutting R using the frontface portion 9 b of the stone, the linear cutting R by the front faceportion 9 b and hence the same cutting as above can be performed bylinearly moving the optical glass material 11 along the W axis aftersetting the angle of the grinding stone 9 to the W axis andappropriately positioning the stone.

[0110] Although the grinding method of the fifth embodiment differs fromthe third embodiment, a polishing trace with a fine regular pattern asobserved in the case of the third embodiment was observed on the surfaceof a glass lens produced by the grinding method of the fifth embodiment.This is because polishing is performed using fine particles. The opticalproperties of the resultant lens were sufficient for various purposes.In other words, the grinding method for simultaneously performinggeneration of a spherical surface and polishing the surface can beexecuted using the conventional curve generator (grinding device). Theother advantages of the fifth embodiment are similar to those of thethird embodiment.

[0111] Although in the fifth embodiment, a flat convex lens is produced,a flat concave lens can be produced if the edge shape of the grindingstone, or the positional relationship between the T axis and the W axisis changed from those shown in FIG. 11 so that a concave shape can beground. Furthermore, if the resultant flat convex or concave lens isheld on the chuck 2 with its reverse surface directed upward, and then aprocess as above is performed, a lens with opposite convex sides orconcave sides can be produced. Although in the fifth embodiment, fineparticles are attached to the grinding stone 9 before the linear cuttingR is performed, they may be attached to the stone 9 when a final surfaceshape is generated after the optical glass material 11 is rotated aboutthe W axis, and the side face portion 9 a as a shape generating face isadvanced into the material 11.

[0112] A sixth embodiment will be described with reference to FIG. 14.

[0113]FIG. 14 is a schematic view, showing a curve generator used in thesixth embodiment.

[0114] The curve generator has the same structure as that used in thefifth embodiment, and hence no explanation is given thereof.

[0115] A grinding method using the curve generator will be describedreferring to FIG. 14. The process performed until the inclination angleof the T axis to the W axis is obtained is similar to that of the fifthembodiment.

[0116] While the grinding stone 9 and the optical glass material 11 arerotated about the T axis and the W axis, respectively, the polishingmaterial 5 is supplied therebetween from the nozzle 6. At this stage, novoltage is applied between the electrode 7 and the grinding stone 9 fromthe DC power 8.

[0117] Subsequently, the grinding stone 9 is moved along the T axis,thereby starting linear cutting R using the front face portion 9 b as ashape generating face, as in the conventional curve generating process.

[0118] When the linear cutting R is continued and then the front faceportion 9 b has reached a line which is defined by theradius-of-curvature 12 of a to-be-generated spherical surface, thelinear cutting R is finished.

[0119] Then, while the linear cutting R is stopped and the positionalrelationship between the grinding stone 9 and the optical glass material11 is kept, i.e. while the spark-out state is maintained, a negativevoltage is applied from the DC power 8 to the electrode 7, and apositive voltage from the DC power 8 to the grinding stone 9 via therotary shaft 4. Silica particles with negative charge, which arecontained in the polishing solution 5 fed from the nozzle 6, areelectrically attracted, as a result of the so-called electrophoresis, bythe grinding stone 9 with the positive voltage, and electricallyattached thereto. Since at this time, the grinding device is in thespark-out state, almost no grinding force acts on the front face portion9 b. Accordingly, most of the electrically attached silica fineparticles do not fall from the grinding stone 9 and are used to polishthe generated spherical surface into a mirror state. In other words, inthe spark-out state, the front face portion 9 b functions as a polishingface. As described above, the spherical surface is generated and thenpolished, which is the termination of working of the flat convex lens.

[0120] Although in the sixth embodiment, the grinding stone 9 islinearly moved along the T axis, thereby performing linear cutting Rusing the front face portion 9 b of the stone, the linear cutting R bythe front face portion 9 b and hence the same cutting as above can beperformed by linearly moving the optical glass material 11 along the Waxis after setting the angle of the grinding stone 9 to the W axis andappropriately positioning the stone.

[0121] Since polishing was performed using silica fine particles, theflat convex lens resulting from the sixth embodiment had sufficientoptical properties, although a fine polishing trace of a regular patternwas observed on the surface of the lens, as in the third embodiment. Theother functions of the sixth embodiment were similar to those of thethird one.

[0122] According to the sixth embodiment, generation of a sphericalsurface and polishing of the surface can be simultaneously performedusing the conventional curve generator. The other advantages of thesixth embodiment were similar to those of the third one.

[0123] Although in the sixth embodiment, the cutting performed by thegrinding stone 9 is linear cutting R, any other cutting manner may beemployed since mirror surface grinding is performed in the spark-outstate after the spherical surface is generated. Moreover, although thisembodiment uses, throughout the cutting process, the polishing material5 which contains silica fine particles with negative charge, a coolantused in the conventional grinding, for example, may be used until thedevice is sparked out. Further, although voltage application to theelectrode 7 is performed in the spark-out state in the embodiment, itmay be done throughout the cutting process.

[0124] Although in the sixth embodiment, a flat convex lens is produced,a flat concave lens can be produced if the edge shape of the grindingstone, or the positional relationship between the T axis and the W axisis changed from those shown in FIG. 11 so that a concave shape can beground. Furthermore, if the resultant flat convex or concave lens isheld on the chuck 2 with its reverse surface directed upward, and thenworking as above is performed, a lens with opposite convex sides orconcave sides can be produced.

[0125] A seventh embodiment which is an application of the third andfourth embodiments will be described with reference to FIGS. 6 to 8referred to for the description of the third embodiment, and also withreference to FIG. 15.

[0126] That part of the process of the seventh embodiment whichcorresponds to FIGS. 6 to 8 is similar to the third embodiment.Specifically, in the seventh embodiment, arcuate cutting θ is performed,as shown in FIG. 8, until the portion of the grinding stone 9 whichcontacts the optical glass material 11 reaches the W axis, with silicafine particles with negative charge electrically attached to thegrinding stone 9 with positive voltage. After the arcuate cutting θ, oneor both of the grinding stone 9 and the optical glass material 11 aremoved to define a clearance L therebetween as shown in FIG. 15. At thetime of defining the clearance L, it is more desirable to move thegrinding stone 9 so that it can have a center-of revolutionsubstantially identical to the center O.

[0127] The clearance L is defined by moving the grinding stone 9 alongthe T axis away from the optical glass material 11, using the stonedriving unit described in the third embodiment, or by moving the opticalglass material 11 along the W axis away from the grinding stone 9, usingthe to-be-processed object driving unit described in the thirdembodiment, or by simultaneously moving both the grinding stone 9 andthe optical glass material 11 away from each other as aforementioned.

[0128] The position of the grinding stone 9 in the direction of itsrevolution with respect to the optical glass material 11, which isassumed immediately after the clearance L is defined, is where thearcuate cutting θ is finished. At this time, the grinding stone 9 andthe optical glass material 11 are rotated in their positions about the Taxis and the W axis by the grinding stone driving unit and theto-be-processed object driving unit, respectively. Even after theclearance L is defined, silica fine particles are attached and built upas a result of the electrophoresis phenomenon. Thus, the clearance L isfilled with the silica fine particles, and the resultant silica layerfurther polishes the generated spherical surface of the optical glassmaterial 11.

[0129] After the polishing by the silica layer which blocks theclearance L is finished, the grinding stone 9 is shifted along the Taxis away from the optical glass material 11 and returned to its initialposition shown in FIG. 6, by its driving unit. At this time, the supplyof the polishing material 5 from the nozzle 6, the voltage applicationby the power 8, and the rotation of the grinding stone 9 and thematerial 11 are stopped, and the resultant flat convex lens is takenfrom the chuck 2.

[0130] In the seventh embodiment, the grinding and polishing of aspherical lens is performed in the same process as in the thirdembodiment, and further polishing is performed only by silica fineparticles built up in the clearance L. The latter polishing caneliminate a defect or flaw on the outward appearance of the resultantspherical lens. In other words, when a grinding stone of a shape asemployed in the second embodiment is used to perform arcuate cutting θof the optical glass material 11, there is always a non-contact portionbetween the grinding stone 9 and the material 11, and a similaradvantage can be obtained from the non-contact portion. However,positive forming of the clearance L made in this embodiment will providea more smooth mirror surface.

[0131] If attachment and growth of the polishing material 5 using theelectrophoresis phenomenon is performed without the clearance L, thebonding material contained in the grinding stone will elute because ofelectrolysis in accordance with the growth of the polishing material 5such as silica. Since the bonding material holds grinding particles suchas diamond particles contained in the grinding stone, the diamondparticles may well fall from the stone when the bonding material haseluted. If they fall from the stone, they rotate between the rotatinggrinding stone and the optical glass material when no clearance L isformed. As a result, flaws may well be formed on the glass materialsurface. On the other hand, where the clearance L is formed, fallendiamond particles are discharged without being kept between the grindingstone and the optical glass material, and only silica particles grown inthe clearance L are put into contact with the material 11 and polish thematerial. As a result, no flaws will be formed on the surface. Forexample, when #600 diamond particles are contained in the grindingstone, the diamond average diameter is 26 to 31 μm. Therefore,occurrence of flaws due to fall of grinding particles can be avoided bysetting the clearance L sufficiently larger than the average diameter.

[0132] It is evident that the clearance L should be set in light of thesize (#) of grinding particles contained in a grinding stone employedand/or the kind of a bonding material used. When, in particular, abonding material which will easily elute is used, the grinding particlesmay well fall. Therefore, a clearance with a width appropriate to theconditions should be defined.

[0133] The optical glass material 11 and the grinding stone 9 may beabruptly moved away from each other so as to set the clearance L atonce, or be moved gradually. If in the latter case, the growth speed ofa silica fine particle layer due to the electrophoresis phenomenon isset higher than the movement speed of the grinding stone and the opticalglass material to gradually enlarge the clearance L, the polishing ofthe optical glass material 11 by the silica fine particles is continuedwithout interruption, thereby enhancing the efficiency of the process.

[0134] When in the seventh embodiment, the grinding stone AD600-N100Mmanufactured by Asahi Diamond Industry Co., Ltd. was used, andelectrophoresis was caused to occur with the voltage set at 40V andcolloidal silica set at 6% by weight, growth at a speed of 0.2 mm/min.was observed. Therefore, if the clearance L is formed at a speed of 0.2mm or less per minute under the above conditions, the growing layer ofsilica fine particles is kept in contact with the optical glassmaterial, whereby efficient polishing of the material is performedwithout interruption.

[0135] A regular polishing trace similar to but finer than that obtainedin the third embodiment was observed on a flat convex lens polished bysilica fine particles.

[0136] As described above, the seventh embodiment can provide advantagessimilar to the third embodiment. Further, it enables more smooth mirrorsurface grinding of a to-be-polished surface since only the layer offine particles grown in the clearance is put into contact with theoptical glass material to be polished. The clearance L further serves toprevent contact of grinding particles of the grinding stone with theoptical glass material, and also to discharge therethrough fallengrinding particles, if any, without putting them into contact with theto-be-worked surface of the optical glass material, thereby to preventforming of flaws on the to-be-worked surface.

[0137] According to an aspect of the invention, a desired shape can begenerated from a material and more smooth mirror surface grinding can beperformed than a grinding stone used therein can, without exchanging thegrinding stone with another. Therefore, the time required from shapegeneration to surface polishing can significantly be reduced.

[0138] According to another aspect of the invention, shape generationusing a shape generating face and polishing using a polishing face canbe performed without exchanging a grinding stone used therein withanother. Therefore, the time required from shape generation to surfacepolishing can significantly be reduced.

[0139] According to a further aspect of the invention, theabove-described advantages can be obtained using the conventional curvegenerator.

[0140] According to yet another aspect of the invention, the number offine particles attached to a polishing face is increased, therebyenabling more improved polishing.

[0141] According to another aspect of the invention, a layer of fineparticles is grown in a clearance, which further improves mirror surfacegrinding of the to-be-polished surface. Moreover, the clearance canprevent grinding particles fallen from the grinding stone, if any, fromdamaging the to-be-polished surface.

[0142] According to still another aspect of the invention, the mirrorsurface grinding enables a lens with excellent optical properties to bemade in a short time and at low cost.

[0143] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalent.

1. A mirror surface grinding method for processing an optical glassmaterial into a desired shape using a grinding stone, comprising thesteps of: supplying the grinding stone with a polishing solution whichcontains charged fine particles, thereby electrically attaching thecharged fine particles to the grinding stone; and rotating and movingthe grinding stone relative to the optical glass material along a finalshape to be generated from the optical glass material, thereby grindingan unnecessary portion of the optical glass material to remove it, usinga side face portion of the grinding stone, and at the same timepolishing the final shape surface of the optical glass material usingcharged fine particles attached to a front face portion of the rotatingand moving grinding stone.
 2. A method according to claim 1, wherein thegrinding stone is cup-shaped such that the front face portion is anannular face portion.
 3. A method according to claim 2, wherein thefront face portion of the grinding stone is tapered from aside-face-portion side toward an axis of the grinding stone.
 4. A methodaccording to claim 1, wherein the front face portion of the grindingstone includes at least two concentric annular face portions ofdifferent levels.
 5. A method according to claim 1, further comprising,after the step of polishing the final shape surface of the optical glassmaterial using the fine particles attached to the front face portion ofthe grinding stone, a step of defining a clearance between the polishedfinal shape surface and the front face portion of the grinding stone byseparating the grinding stone from the final shape surface, and furtherpolishing the final shape surface using fine particles attached to thefront face portion.
 6. A mirror surface grinding method for processingan optical glass material into a desired shape using a grinding stone,comprising the steps of: supplying the grinding stone with a polishingsolution which contains charged fine particles, thereby electricallyattaching the charged fine particles to the grinding stone; linearlycutting the optical glass material by a front face portion of thegrinding stone until the front face portion reaches a portion of theoptical glass material from which a final shape surface is to begenerated, while rotating the grinding stone; and rotating the opticalglass material after finishing the linearly cutting, and rotating andmoving the grinding stone relative to the optical glass material along afinal shape to be generated from the optical glass material, therebygrinding an unnecessary portion of the optical glass material to removeit, using a side face portion of the grinding stone, and at the sametime polishing the final shape surface of the optical glass materialusing charged fine particles attached to the front face portion of therotating and moving grinding stone.
 7. A method according to claim 6,wherein the grinding stone is cup-shaped.
 8. A method according to claim6, wherein the step of electrically attaching the fine particles to thegrinding stone is performed when the front face portion of the grindingstone has reached at least a portion of the optical glass material fromwhich the final shape surface is to be generated.
 9. A method accordingto claim 6, further comprising, after the step of polishing the finalshape surface of the optical glass material using the fine particlesattached to the front face portion of the grinding stone, a step ofdefining a clearance between the polished final shape surface and thefront face portion of the grinding stone by separating the grindingstone from the final shape surface, and further polishing the finalshape surface using fine particles attached to the front face portion.10. A mirror surface grinding method for processing an optical glassmaterial into a desired shape using a grinding stone, comprising thesteps of: rotating at least one of the grinding stone and the opticalglass material and at the same time linearly cutting the optical glassmaterial by a front face portion of the grinding stone until the frontface portion reaches a portion of the optical glass material from whicha final shape surface is to be generated; and supplying the grindingstone with a polishing solution which contains charged fine particles,when the front face portion of the grinding stone has reached at leastthe portion of the optical glass material from which the final shapesurface is to be generated, and polishing the final shape surface usingthe fine particles attached to the front face portion of the grindingstone while rotating both the grinding stone and the optical glassmaterial, after the step of electrically attaching the fine particles tothe grinding stone and the step of the linear cutting.
 11. A methodaccording to claim 10, wherein the grinding stone is cup-shaped.
 12. Amethod according to claim 11, further comprising a step of inclining anaxis of rotation of the optical glass material and an axis of rotationof the grinding stone at angles determined from a swivel angle employedin the case of a curve generator.
 13. A method according to claim 10,wherein the step of polishing the final shape surface by the fineparticles is performed with the positional relationship between thegrinding stone and the optical glass material maintained, after thelinear cutting is finished.
 14. A method according to claim 10, whereinthe step of polishing the final shape surface by the fine particles isperformed with a clearance defined between the grinding stone and theoptical glass material, after the linear cutting is finished.
 15. Aglass lens ground by the grinding method described in claim 1, which hasa polishing trace formed on its surface by fine particles attached tothe grinding stone as a result of the electrophoresis phenomenon, thepolishing trace having a regular pattern and a depth of 10 nm or less.16. A glass lens ground by the grinding method described in claim 6,wherein the front face portion of the grinding stone includes at leasttwo concentric annular face portions of different levels.
 17. A glasslens ground by the grinding method described in claim 10, wherein thefront face portion of the grinding stone includes at least twoconcentric annular face portions of different levels.
 18. A mirrorsurface grinding method for processing an optical glass material into adesired shape using a grinding stone, comprising the steps of: preparinga grinding stone which has a shape generating face for cutting theoptical glass material to thereby grind the optical glass material, anda polishing face for polishing a surface generated by the shapegenerating face; holding the optical glass material on holding means;supplying a polishing solution which contains charged fine particles,between the grinding stone and the optical glass material; and moving atleast one of the grinding stone and the optical glass material relativeto each other, cutting the optical glass material by the shapegenerating face of the grinding stone to thereby grind the optical glassmaterial into a desired shape surface, and at the same time polishingthe desired shape surface by the fine particles attached to thepolishing face of the grinding stone, while electrically attaching fineparticles to the grinding stone on a continuous basis.
 19. A methodaccording to claim 18, wherein the grinding stone is cup-shaped.
 20. Amethod according to claim 18, further comprising, after the step ofpolishing the desired shape surface, a step of separating the grindingstone from the optical glass material, and continuing polishing usingfine particles attached to the polishing face of the grinding stone. 21.A mirror surface grinding method for processing an optical glassmaterial into a desired shape using a grinding stone, comprising thesteps of: preparing a cup-shaped grinding stone which has a shapegenerating face for cutting the optical glass material to thereby grindthe optical glass material, and a polishing face for polishing a surfacegenerated by the shape generating face; holding the optical glassmaterial on holding means; supplying a polishing solution which containscharged fine particles, between the grinding stone and the optical glassmaterial; and moving at least one of the grinding stone and the opticalglass material relative to each other, and cutting, using a front faceportion of the grinding stone, the optical glass material to a portionof the material from which a desired shape surface is generated; andmoving at least one of the grinding stone and the optical glass materialrelative to each other, and cutting, using a side face portion of thegrinding stone, the optical glass material into the desired shapesurface, and at the same time polishing the desired shape surface by thefine particles attached to the front face portion of the grinding stone,while electrically attaching fine particles to the grinding stone on acontinuous basis.
 22. A method according to claim 21, furthercomprising, after the step of polishing the final shape surface of theoptical glass material using the fine particles, the step of defining aclearance between the polished final shape surface and the grindingstone by separating the grinding stone from the optical glass material,and further polishing the final shape surface using fine particlesattached to and grown on the front face portion of the grinding stone.23. A glass lens obtained by rotating a grinding stone and an opticalglass material, moving them relative to each other, thereby grinding theoptical glass material by the grinding stone, the glass lens having atrace of a regular pattern.
 24. A glass lens according to claim 23,wherein the regular pattern consists of a group of striped polishingtraces.